[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

GBlist: Fwd: Windows and stuff....



oops!  forgot to send to the group.
---------------------
Forwarded message:
Subj:    Windows and stuff....
Date:    97-08-28 13:52:20 EDT
From:    RCMathis1
To:      brucecol@crocker.com

Bruce wrote:

<< The 'pultruded' fiberglass reinforce resin sash and frame (the Fibertherm
 technology) is very strong and has the same coef. themal expansion (low) as
 glass, therfore the seals are not stressed in regions with high temp
 variations.  The lowness of the CTE also means that the sashes are less
 inclined (than vinyl for example) to bow out of the frame on really cold
 periods thereby breaking the seals/ promoting air leakage.  (I understand
 that standard air tightness test for windows are perform *without* a temp
 difference across the window - inside to outside .... am I correct in this
 understanding? any comments from the gallery?) >>

Bruce,

Thanks for the extra information and I will follow-up with the contacts
provides.  

First, to your point about coefficients of thermal expansion, you are RIGHT
to be concerned about differentials and sash and frame movement.  The same
concerns exist (sometimes to a greater extent) the hotter the climate!
 (That's why straight PVC doesn't fair so well in Phoenix....)  Often
composite technologies were developed to address just this problem and
typically have a decided advantage over other framing materials in this
regard....

And about those air leakage tests.... RIGHT AGAIN.  Window and door air
leakage has (historically) NOT been tested at a temperature difference.  The
industry standard ASTM test is pressure difference only.  NFRC and others
have been looking more closely at this issue.  Laboratories and scientists in
the US and Canada have been working on developing a standard procedure to
conduct tests at both a temperature AND pressure difference .  Stay tuned for
more developments.... IN THE MEAN TIME, be skeptical about the accuracy of
air leakage performance claims.  Many window manufacturers only have to
conduct a single test every four years to make an air leakage claim!  

Finally, don't rely on existing window air leakage performance values to do
detailed energy calculations in climates with big temperature differences.
 AND PLEASE do not rely on window air leakage as the only means for meeting
fresh air needs....

End of rant.

Chris Mathis
MCSquared
5249 Columbia Road
Columbia, MD  21044
301-596-1931

______________________________________________________________________
This greenbuilding dialogue is sponsored by CREST <www.crest.org>
Environmental Building News <www.ebuild.com> and Oikos <www.oikos.com>
For  instructions send  e-mail to  greenbuilding-request@crest.org.
______________________________________________________________________